1. Technical Field
The present invention relates to a resistance film type input device capable of detecting a touch position of a finger or the like and a display device with an input function, which includes the resistance film type input device.
2. Related Art
In electronic apparatuses such as mobile telephones, car navigation systems, personal computers, ticket vending machines, bank terminals or the like, recently, there is provided an electronic apparatus in which an input device called a touch panel is provided on the surface of a liquid crystal device or the like such that information can be input by referring to an image displayed in an image display region of the liquid crystal device. Among input devices, in a resistance film type input device, planar electrodes are formed over whole input regions of a first light transmission substrate and a second light transmission substrate which face each other, and band-shaped electrodes are electrically connected to the ends of such planar electrodes.
In such a resistance film type input device, a voltage is applied to a planar electrode via a band-shaped electrode so as to detect a contact position. Accordingly, if a sufficient resistance difference is not generated between the resistance value of the planar electrode and the resistance value of the band-shaped electrode, linearity of a position and an electrical signal which can be obtained by an input position detecting circuit deteriorates. However, recently, a region called a frame at the outer circumference of the input region tends to be narrowed and thus the width of the band-shaped electrode needs to be narrowed. Accordingly, the sufficient resistance difference cannot be ensured between the resistance value of the planar electrode and the resistance value of the band-shaped electrode. If the thickness of the planar electrode is reduced, a variation in in-plane resistance is increased, and the planar electrode is damaged while an input operation is repeated, such that the detection of the input position cannot be accurately performed. Thus, reliability deteriorates.
Accordingly, a configuration in which a plurality of openings with 70 μm square is formed in a planar electrode such that a sheet resistance value of the planar electrode is increased by about 2.4 times to 2.5 times is suggested (see JP-A-2001-34419).
However, as described in JP-A-2001-34419, if the openings with 70 μm square are formed, the openings are conspicuous when the resistance film type input device is viewed from the top and the quality of the input device deteriorates. In particular, if an image generating device is arranged on a rear surface of the resistance film type input device so as to configure a display device with an input function, when the openings are conspicuous, an image generated by the image generating device cannot be viewed in a high quality state. In addition, since such a problem becomes more serious if the size of the openings is increased in order to further increase the sheet resistance value of the planar electrode, it is difficult to further increase the sheet resistance value of the planar electrode.